My bins parameters?

[pipnina]

I have a pair of binoculars that used to be my great grandad's (Perl 10x50s) and because of this, I can't just look up the specs like exit pupil, AFOV etc anc I would need some help.

The binoculars are 10x50 and have an 8 degree FOV, with this, how do i work out the exit pupil and the AFOV of the eyepieces?

Thanks,

    ~pip

[Charic]

....divide the Aperture by the Magnification to obtain the Exit Pupil.

therefore.......10x50  ~  50/10=5mm exit Pupil. If you square this you end up with 25 as the relative brightness of the optics ( if / when comparing to other optics )

The real field is 8° The AFOV is the real field multiplied by the magnification, therefore  8*10= 80° AFOV

There is also another datum? 10x50= 500 sq.root =22.4 twilight Factor / detail observed in low light ( again, only useful when comparing between different optics )

[ronin]

As exit pupil is Objective/Mag then it looks like 50/10 = 5mm exit pupil.

Got to go recall which one AFOV is. :eek:

Quick look up:

TFOV = AFOV/Mag.

Your TFOV is 8 degrees, as the Mag is 10 then the AFOV would be 8x10 = 80.

Which seems a bit much - do binoculars work in terms of the maths the same as a scope?

Just thinking that the normal use is to "merge" the image from each half into one, so you may get a sort of artifically high TFOV.

[pipnina]

....divide the Aperture by the Magnification to obtain the Exit Pupil.

50/10=5mm exit Pupil 

As exit pupil is Objective/Mag then it looks like 50/10 = 5mm exit pupil.

Got to go recall which one AFOV is. :eek:

Thanks guys! Now I just need to find AFOV.

[John]

If the true field of view (TFoV) is 8 degrees the apparent field of view (AFoV) would be 80 degrees.  Sounds high to me. Most 10x50 binoculars are 6-7 degrees TFoV which is 60-70 degrees AFoV. Not all binoculars deliver what is written on them though !

[pipnina]

If the true field of view (TFoV) is 8 degrees the apparent field of view (AFoV) would be 80 degrees.  Sounds high to me. Most 10x50 binoculars are 6-7 degrees TFoV which is 60-70 degrees AFoV. Not all binoculars deliver what is written on them though !

Just did some measuring in stellarium and it does manage minimum 7 degrees TFOV (but likely more) (I knew I could fit just more than the three pointer stars of cassiopeia (that I follow down to M31) in the FOV, stellarium says that distance is at leat 7 degrees across and 8 if there's a little wiggle room either side)

P.s. what are you doing to work out the AFOV?

[Astrobits]

AFOV is simply True FOV x magnification.

I agree with John, 80 AFOV seems a bit big. You could check all the stats by doing some measurements yourself:

Set the bins up, focussed on infinity or thereabouts, so they are pointing at a bright surface, Then measure the exit pupil with some thin graph paper or just make some pencil marks to match the exit pupil dia. Then measure the clear objective diameter. Divide one by the other to get the magnification.

For TFOV you have already done that but try to get a more accurate value.

Nigel

[pipnina]

AFOV is simply True FOV x magnification.

I agree with John, 80 AFOV seems a bit big. You could check all the stats by doing some measurements yourself:

Set the bins up, focussed on infinity or thereabouts, so they are pointing at a bright surface, Then measure the exit pupil with some thin graph paper or just make some pencil marks to match the exit pupil dia. Then measure the clear objective diameter. Divide one by the other to get the magnification.

For TFOV you have already done that but try to get a more accurate value.

Nigel

Thanks, I'll try that.